There are challenges to luring a movie star back to a film sequel — even dolphins, apparently. Director Charles Martin Smith found this out after 2011's Dolphin Tale proved to be a breakout vehicle for his aquatic star, Winter.

"Winter had some demands, she knows she's a star now," jokes Smith. "I did have to throw in some higher-quality herring. She wants it fresh."

No matter how much herring is required, it was worth it for Dolphin Tale 2 (out Sept. 19).

In 2005, the 5-month-old Winter became caught in a crab trap in an accident that destroyed her crucial tail flukes. It was a dire situation for the dolphin; she struggled for life while under care at Florida's rescue center, the Clearwater Marine Aquarium.

"When she lost her tail, there was some talk of perhaps putting her down. No dolphin had ever survived this way," says Smith. "But the people who worked with Winter saw such life and spirit in her. They fought to keep her alive."

A leading prosthetic expert heard about her plight and built an artificial fin to allow Winter to swim properly, inspiring the movie that starred Winter, Harry Connick Jr., Kris Kristofferson, Ashley Judd and Morgan Freeman.

The same spirit that kept Winter alive made her a natural star on film. Winter also remains a standout at the Clearwater Marine Aquarium, where fans still flock daily to visit. In Dolphin Tale 2, Smith took four new real-life situations from the aquarium and weaved them into another tale around Winter.

In the new film, Winter's surrogate mother, Panama, dies, leaving the dolphin in a mourning funk requiring Connick Jr (as the aquarium's Dr. Clay Haskett) to seek out another pool companion among dolphins in need of care. Bethany Hamilton, who had her left arm bitten off by a shark while surfing in 2003, also appears in the film as herself — the two bond over their shared obstacles.

Winter seemed to exhibit overt happiness to be shooting another film that featured much of the original cast, including Freeman as the eccentric prosthetic expert Dr. Cameron McCarthy. Freeman says he got a special greeting from the mammal when he showed up on the set.

Ashley Judd returns as Lorraine Nelson and Morgan Freeman as Dr. Cameron McCarthy. Freeman says he and the dolphin star have developed a special bond.(Photo: Wilson Webb, Warner Bros. Pictures)

"She gave a whistle for me," says Freeman. "You know she recognizes you. You cannot help but to talk to her. We just don't realize how intelligent other forms of life are."

Smith says Winter loved the attention the filming brought and would make noises from the pool during scenes in which she wasn't featured.

"She'd go to the edge of the pool and whistle. It was like, 'What about me?' She always wanted to be included," says Smith. "I'm convinced she knows when the camera is pointed in her direction. She is a bright animal and she gets it."

Should the formula continue to work on the big screen, filmmakers will truly have to dig deep around negotiation time with Winter for future sequels.

"I don't think it will really go to her head actually," says Smith. "As long as the quality of the fish remains the same and the love and care she gets stays the same, she's going to be happy. Winter is a true sweetheart."